Conventionally, for such a heating device, there is known a device disclosed in PATENT DOCUMENT 1 (Japanese Unexamined Patent Publication No. 2009-30771). In this heating device, a wiring passage is formed in a solderless terminal. A wire heater is inserted from an opening of the wiring passage, a lead wire is inserted from the opposite opening of the wiring passage, and the wire heater and the lead wire are connected in the wiring passage. Since waterproofing should be performed for the connecting portion, the inside portions of the two openings of the wiring passage are provided with sealing members. 